Method of making seamless tubes



Nov. 20, i923 R. C. STIEFEL METHOD OF MAKING SEAMLESS TUBES Filed June 16@ 1920 III Hnmm

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METHOD OF MAKING SEAMLESS TUBES.

Application med June 1e, 1920. serial No. 389,348;

To all 'whom t may concern.'

Be it known that-I, RALPH C.. S'rrEFrL, a citizen of the United States, and a resldent -of Ellwood City, in the county of Alleis therein reduced to a blank having a wall thickness and diameter substantially that of the desired finished tube, and said tube is then cross rolled or reeled over a mandrel to smooth out any interior grooves or ridges and exterior roughness produced in Athe plug-mill, true the gageand round the tube.

In the reeling step no material reduction of wall thickness or change in diameter is made, due to the character of the rolls employed, and theiraction. Consequently the entire reduction in wall thickness must be made in the piercing and plug-rolling operations, and since in the plug-rolling operation the blank is'brought down to the desired finished wall thickness it cools quite rapidly so that there is a limit to the number of passesiwhich can be given in the plug-mill. This has necessitated piercing the billet to as thin a wall as is practical, in order that it can be reduced to the finished wall thick ness in a limited number of passes which can be given in the plug-mill before the blank cools excessively. Piercing thesolid billet to a thin wall obviously produces a heavy stra-in on the steel', and is liable to tear it, but in any event to aggravate an)v seams or defects existing in the solid steel billet. Y

Furthermore, while in the piercing opera tion the diameter of the bla-iik can be increased to a limited extent beyond that ot' the solid billet, such slight increase in diameter is offset in the plug-rollin where the effect is to reduce the iameter of the blank while thinning and elongating it, and in the reeling operation, as already operation stated, there is no material increase in diameter. Consequently in all cases the solid billet must be of substantially the same diameter as the finished tube, as a result of which the method does not lend -itself well tothe production of tubes of large diameter, and for any vgiven size of tubes leads to a large percentage of rejections due to dcfects in the metal, as will hereinafter appear.

My improved method, generally stated, comprises the steps of piercing the solid billet,- then plug-rolling the hollow blank, 'and then subjecting the blank to the action of cross rolls of the kind known asexpanding rolls, which latter step still further and very substantially reduces thethickness of the walls and increases the diameter of the tube, while at the same time eliminating or reducing any scores or irregularities and smoothingthe tube both internally and externally. Because in this cross-rolling operation the wall thickness is substantially reduced, it is not necessary to bring the blank to the lexpanding rolls with its walls reduced to substantially the finished gage. Consequently the billet can be pierced with a thicker wall, thus imposing less strain on the steel, and also giving a blank which is softer and at a better rolling heat than with theold thin walled pierced billets, and which therefore can be more quickly and easily reduced in the plug-mill and with a better' effect on the metal. l4`i11'tl1ci1no-ie. since inthe plugrolling the blank is not reduced to the desired finished wall thickness it also goes t0 the cross rolls at a higher'temperature than in the existing method, and can therefore. be e'ectively andeasily reduced to the final desired gage. I'wncein the expanding rolls the tube is substantially increased in diameter this method, for a given size of tube, permits of the use of a billet of less diameter than is possible under the old method. This has important advantages as will hereinafter appear.

In the accompanying drawings Fig. 1 illustrates diagrammatic-ally the piercing operation; Fig; 2 similarly illustrates the plug-rolling operation; and Fig. 3 similarly illustrates the cross-rolling and expanding operation.

The piercing mill may be of any desired type, that shown in Fig. 1 comprising a pair of barrel shaped rolls 5 provided with the usual pass which first converges and then diverges and having lying in the exit side of the pass the usual piercing plug or point The solid billet 7 is here pierced and son'iewhat expanded, forming n hollow blank 8 which ditl'els from the usual pierced blank only in that it need not be reduced to as thin a wall as has heretofore been the practice.

The pierced blank then goes to the plugrolling mill which may be of any desired form, that shown in Fig. 2 comprising a pair of grooved rolls 9 provided with a plurality of passes in whichlie suitable plugs 10-heldv by bars l1. In this mill the hollow blank is given one or more passes, as necessary, preferably a plurality of passes, and is reduced therein to wall thickness substantially greater than that of the desired finished tube. This mill will be so organized that the several passes therethrough follow each other in quick succession, to secure the necessary reduction with as little loss of heat as possible. In this mill the blank is'not only elongated and the walls thinned, but because of the relative high temperature of the blank during this operation any seams or Odefects inherent in the steel and aggravated in the piercing operation, or produced by the piercing operation, are closed and Welded to a greater extent than with the thinner and colder blanks which are plug-rolled under the old process.

' The blank 12 then goes to the cross-rolling or expanding mill, shown in Fig. 3,' cmprising the conical' rolls 13 (or their equivalent) which provide a pass which slightly converges at the entrance side and materially diverges on the delivery side and having lying 1n such pass on the delivery side the conical plug 14 yheld by the bar 15. In this nill the blank is very substantially expanded, thus producing a substantial reduction in wall thickness and an increase in diameter, and is therein reduced to the desired inished wall thickness and diameter.- At the same time the cross-rolling under the external rolls and internal mandrel eliminates any interior grooves or scores and external rough` ness produced in the plug rolling operation, thus smoothing the tubeinside and outside, and also equalizes and ltrues the wall thickness and rounds the tube, so that the tube delivered is commercially sal-able as a hot tini'sh'ed tube.

The several mills described will be so arranged that the blank can be quickly and conveniently transferred from one to the other, in order that the heat may be conserved. The entire, rolling operation de scribed can be readilyv performed at the ini'- tial heatof the billet, but if necessary the blank can be reheated'between operations.

From the cross-rolling or expanding miil the tube is preferably passed through the well-known sizing rolls to reduce it tov exactly the desired diameter. l WVhere tubes of 'icross-rolling ste-p the blank is very substam tially increased in diameter, it is possible for any given sized tube to start with a solid billet of less diameter than the old method.

rIlhis is not onl' a great advantage in theA manufacture of large diameter tubes but for any (viven size of tubes the billet will be sounder and will have less seams or defects, or at least of less depth, than the corresponding billet which is necessary under the old method, because in steel mill practice the billets are produced from standard sizes ofv ingots, and manifestly the smaller the diameter of the billet the greater the amount of rolling necessary to bring it to size and consequently the more work expended on thesteel and the betterP the quality of the steel. Any seams or other-'defects existing in the ingot are less, and are of relativ-,ely less dept-h in a small sized billet than in a large sized billet rolled from the same ingot. It isalso of great advantage to pierce with thick walls as'thereby the metal is tortured less and hence the defects inxthe steel are aggravated to a lesser extent. than underfthe old method, and tearing and seaming of the metal yis also largely avoided. The thick walled hollow billet has the further obvious advantage that it will hold its heat more effectively than a thin walled hollow billet, and consequently it is softer and at a better rolling temperature for plug-rolling so that the latter step can be more easily and quickly' carried out and in addition any defects in the metal or `seams which'may have `been produced in the piercing 'operation are, bythecompressing l f action on the 'metal while confined lbetween the. rolls or grooves on the outside A"and the Y' plug or mandrel on the inside, closed and l.

welded more effectivel and' to a greater extent than under the ol( method. The net result is that the percentage of rejections due to defects or seams in thetubes is much less than under the old method. 'i Furthermore,v because the tube isnot reduced to the desoftness of` the thicker lportion of the tube wall.

I claim.:4

l. The method of making seamless tubes which consists in rolling a relatively thick Walled hollow billet in a plug-mill to a tube of less diameter and greater wall thickness than the -desired finished tube and simultaneeter and `Wall thickness, and simultaneously smoothing the tube inside' 'and outside,

.rounding it, and truing and equalizing its Walls.

2. IThe method of .making seamless'tubes which consists nY lpiercing a solid billet to form a relatively thick Walledeblenk, then i rolling said blank in a plug-mill and thereby gelongfating and thinning its walls and producing a blank of less diameter and greater Wall thickness than the desired tube, and lthen cross-rollingV and expanding said blank over a mandrel plug in a manner to reduce its wall thcimess and increase its diameter to the desired Wall thickness and diameter, and simultaneously smoothing the tube internally and externally, rounding it, and truing and equalizing its walls.

in testimony whereof, I have hereunto set- I'ny hand.

RALPH o. STIEFEL. a

i Witness:

' HOWARD T. SNIVELY. 

